1. Field of the Invention
The present invention relates to the field of electronic technology, and more particularly to a power frequency modulation (PFM) circuit and a power adapter of an electronic device such as a liquid crystal display (LCD), a television (TV) or a light emitting diode (LED) lamp.
2. Description of the Related Art
To provide an appropriate and stable power to an electronic device, the electronic device is usually equipped with a power adapter. In general, a conventional power adapter controls the connection of a MOS tube by detecting a zero crossing of a secondary current. If the ON time of the MOS tube is a default time, the MOS tube is controlled to be disconnected, so that the critical operating mode of the power adapter can be achieved by detecting the zero crossing of current by a hardware circuit. However, the conventional methods are unable to control the time of the zero crossing of current precisely or the ON time of the MOS tube, so that the timing for switching the operating status of a power adapter cannot be controlled precisely.